Set whether iPhone updates the date and time automatically. Go to Settings > General > Date & Time, then turn Set Automatically on or off. If you set iPhone to update the time automatically, it gets the correct time over the cellular network and updates it for the time zone you're in. Some carriers don't support network time, so in some areas iPhone may not be able to automatically determine the local time.

Set the date and time manually. Go to Settings > General > Date & Time, then turn off Set Automatically.

Set whether iPhone shows 24-hour time or 12-hour time. Go to Settings > General >Date & Time, then turn 24-Hour Time on or off. (24-Hour Time may not be available in all areas.)